Effects of Cu-contaminated soil on Robinia pseudoacacia L.: a controlled environment experiment

The long generation times of trees are a challenge for research, yet trees are exceptionally well-characterized in adaptive quantitative variations and their responses to different environmental variables. Nevertheless, there is a lack of knowledge concerning important early fitness components of germination and establishment, and how different environmental parameters affect ecophysiological traits. Meanwhile the crucial role of soil temperature on plant metabolism, even under stress condition, is underrated in research. Heavy metal contamination in soil affects plants inducing several morphological, physiological, and biochemical dysfunctions. Copper (Cu), while is an essential micronutrient for plants, may cause the cited dysfunctions affecting plant growth when exceed a certain threshold, primarily due to human activities. This research aims to explore how Cu affects the early stage of tree growth, focusing on black locust (Robinia pseudoacacia L.), in controlled environment, with a special attention to soil and air temperature. This is of interest as in the north-eastern Po plain black locust commonly grows along the embankments of railway lines, where we have found that soils are frequently Cu-contaminated. In this research, we are testing black locust seedlings growing under Cu-toxic levels in a controlled environment using a new-concept Microcosm device (European patent no. 3236741). Microcosm setup allows for autonomous control of the environmental conditions of both hypogeal and epigeal portion of the tree. The experiments last 3 months and compare the growth of 2-months old seedlings growing in CuSO4 contaminated soil and in control media (non-contaminated soil). Biomass allocation patterns, allometric relationships, and photosynthetic activity are measured to investigate tree responses at morphological and ecophysiological levels. Cu content is determined in tree samples from each organ using ICP-OES to assess plant potential for phytoremediation purposes. Preliminary results suggest a significant impact on tree growth despite the high tolerance of black locust to highly Cu-contaminated soil.